CN109520208B - Polyolefin device exhaust gas recovery system coupling waste heat refrigeration technology and expansion cryogenic separation technology - Google Patents

Polyolefin device exhaust gas recovery system coupling waste heat refrigeration technology and expansion cryogenic separation technology Download PDF

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CN109520208B
CN109520208B CN201811184870.3A CN201811184870A CN109520208B CN 109520208 B CN109520208 B CN 109520208B CN 201811184870 A CN201811184870 A CN 201811184870A CN 109520208 B CN109520208 B CN 109520208B
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gas
liquid separator
unit
inlet
cryogenic separation
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CN109520208A (en
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廖祖维
董轩
黄正梁
杨遥
蒋斌波
孙婧元
王靖岱
阳永荣
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Zhejiang University ZJU
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0605—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the feed stream
    • F25J3/062—Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/064—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of CnHm with 2 carbon atoms or more
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/066—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0695—Start-up or control of the process; Details of the apparatus used
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/12—Refinery or petrochemical off-gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/04—Compressor cooling arrangement, e.g. inter- or after-stage cooling or condensate removal
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/30—Compression of the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2260/00—Coupling of processes or apparatus to other units; Integrated schemes
    • F25J2260/02—Integration in an installation for exchanging heat, e.g. for waste heat recovery
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/04—Internal refrigeration with work-producing gas expansion loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/906—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by heat driven absorption chillers

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Separation By Low-Temperature Treatments (AREA)
  • Sorption Type Refrigeration Machines (AREA)

Abstract

The invention discloses a polyolefin device exhaust gas recovery system coupling a waste heat refrigeration technology and an expansion cryogenic separation technology. The system comprises: the compression and condensation unit is used for receiving the exhaust gas from the polyolefin device, and recovering heavy hydrocarbon in the exhaust gas after two compression, condensation and gas-liquid separation processes; the cryogenic separation unit receives the gas phase composition of the compression condensation unit and recovers the low-carbon hydrocarbons by expansion self-cooling; and the absorption refrigeration unit recovers the heat energy of the compression condensation unit by adopting a lithium bromide solution intermediate medium to prepare low-temperature cold energy and transmits the low-temperature cold energy to the cryogenic separation unit. The invention generates cold energy at 7 ℃ by recovering the compression heat of the compressed exhaust gas for the deep cooling process of the exhaust gas, reduces the self temperature of the exhaust gas by the expansion process, realizes self-cooling, and further reduces the heat energy emission and cold energy requirements of the recovery process of the exhaust gas of the polyolefin device.

Description

Polyolefin device exhaust gas recovery system coupling waste heat refrigeration technology and expansion cryogenic separation technology
Technical Field
The invention belongs to the field of deep energy conservation of exhaust gas recovery, and particularly relates to a polyolefin device exhaust gas recovery system coupling a waste heat refrigeration technology and an expansion cryogenic separation technology.
Background
In the production process of polyolefin process, the tail gas contains a large amount of unreacted ethylene, propylene, isopentane and high-carbon hydrocarbons besides nitrogen, and if the tail gas is not recovered, a large amount of raw material components are wasted and economic loss is caused, so that the recovery of the exhaust gas of the polyolefin plant is an important component of the polyolefin process, and currently adopted recovery methods comprise a compression condensation method, a membrane separation method, a pressure swing adsorption method, an expansion cryogenic separation method and the like. Compared with other recovery methods, the expansion cryogenic separation technology is characterized in that: the tail gas is expanded and refrigerated through a turbine expander by utilizing the original pressure energy of the discharged gas, and the temperature of the raw material tail gas can be reduced to-120 ℃ by utilizing the cold energy generated by expansion and the heat exchange of the material, so that low-hydrocarbon substances such as ethylene and the like are separated from nitrogen and the like, and the recovery of the ethylene and the like is realized. Has the advantages of low energy consumption, convenient operation, high recovery rate of low-carbon components and the like.
Patent CN 104792117B discloses an apparatus and method for recovering exhaust gas in olefin polymer production, which adopts a combination of compression condensation and double-expansion cryogenic separation to recover hydrocarbon substances in the exhaust gas with high efficiency, thereby obtaining hydrocarbons with high recovery rate and reducing energy consumption. The use of the double-expansion cryogenic separation technology realizes self-cooling of the discharged gas stream from 5 ℃ to-120 ℃, and analysis from the perspective of cold public engineering shows that the circulating cooling water can be used when the temperature reduction requirement of the discharged gas is higher than 35 ℃ in the recovery process of the discharged gas, the expansion self-cooling process can only meet the condition that the stream is condensed from 5 ℃ to-120 ℃, and the temperature reduction of the stream from 35 ℃ to 5 ℃ still needs a large amount of refrigerant. In the compression and condensation process, a large amount of compression heat higher than 100 ℃ becomes waste heat, and the exhaust gas needs to be cooled and condensed by using cold public works, so that the exhaust gas recovery method still has the energy-saving potential.
Disclosure of Invention
The invention aims to further reduce the amount of public works and improve the economic benefit in the existing exhaust gas recovery process adopting the expansion cryogenic technology, and provides a polyolefin device exhaust gas recovery system coupling the waste heat refrigeration technology and the expansion cryogenic separation technology, which comprises a compression condensation unit, a cryogenic separation unit and an absorption refrigeration unit. The method realizes the high-efficiency recovery of hydrocarbon substances and further reduces the heat energy discharge and cold energy requirements of the recovery process of the discharged gas of the polyolefin device by the cooperative cooperation of the compression condensing unit, the cryogenic separation unit and the absorption refrigerating unit.
The invention provides a polyolefin device exhaust gas recovery system coupling a waste heat refrigeration technology and an expansion cryogenic separation technology, which comprises:
a compression condensing unit for receiving the vent gas from the polyolefin plant, recovering heavy hydrocarbons in the vent gas, and outputting a residual vent gas stream;
the cryogenic separation unit receives the gas phase stream of the compression and condensation unit, recovers low-carbon hydrocarbons (mainly ethylene) and outputs residual discharge gas stream;
and the absorption refrigeration unit is used for recovering the heat energy of the compression condensation unit to prepare low-temperature cold energy and conveying the low-temperature cold energy to the cryogenic separation unit.
The system realizes the same hydrocarbon recovery efficiency as that of the patent CN 104792117 by the cooperative matching of the compression condensing unit, the cryogenic separation unit and the absorption refrigerating unit, and reduces the cost of cold energy public engineering and waste of waste heat. The recovery rate of C4+ high carbon hydrocarbon in the exhaust gas is about 100%, the recovery rate of C2 low carbon hydrocarbon is more than 90%, the recovery rate of nitrogen is more than 80%, the waste heat of the compression and condensation unit is reduced by 60%, the efficiency of cold energy prepared by waste heat is 80%, and the cold public works completely use the circulating cooling water with low price, thereby removing the use of the refrigerant.
According to a specific embodiment of the invention, the compression and condensation unit comprises a two-stage or multi-stage compressor-condenser-gas-liquid separator process; in the process of the same stage of compressor-condenser-gas-liquid separator, the outlet of the compressor is connected with the inlet of the hot end of the generator of the absorption refrigeration unit, the heat released by the generator enters the condenser of the same stage, the outlet of the condenser is connected with the inlet of the gas-liquid separator, and the gas-liquid outlet of the gas-liquid separator is connected with the compressor of the next stage; the outlet of the polyolefin device is connected with the inlet of a compressor in the process of a first-stage compressor-condenser-gas-liquid separator; the gas-liquid separator of the last stage compressor-condenser-gas-liquid separator process delivers the gas phase to the cryogenic separation unit.
According to the specific embodiment of the invention, the condenser is a shell-and-tube condenser, the cold medium is circulated cooling water and a refrigerant, and the gas-liquid separator separates high-carbon hydrocarbons in a liquid phase.
According to a specific embodiment of the present invention, the cryogenic separation unit comprises a multi-stream heat exchanger, a gas-liquid separator and an expander. The residual exhaust gas conveyed by the compression condensing unit is connected with a hot end inlet of the multi-strand heat exchanger, a hot end outlet of the multi-strand heat exchanger is connected with a gas-liquid separator inlet, a gas-liquid separator gas-phase outlet is connected with an expander inlet, a gas phase enters a cold end of the multi-strand heat exchanger after being expanded and cooled by the expander, and after cold energy is released, the gas phase goes to a torch to perform tail gas treatment. And a liquid phase outlet of the gas-liquid separator is connected with the other cold end inlet of the multi-flow heat exchanger through an expansion valve, and the low-carbon hydrocarbons are obtained by heating.
According to the specific embodiment of the invention, in the cryogenic separation unit, the exhaust gas is cooled to-120 ℃ through the multi-flow heat exchanger, and the cold energy is obtained from a-130 ℃ low-temperature stream obtained by gas phase expansion cooling and 7 ℃ low-temperature water output by the waste heat refrigeration unit.
According to the specific embodiment of the invention, the absorption refrigeration unit comprises a generator, a gas-liquid separator, a condenser, an evaporator, an absorber and a stream heat exchanger, wherein an intermediate medium in the absorption refrigeration unit is connected with a cold end inlet of the generator to absorb heat from a compression condensation unit; the outlet of the cold end of the generator is connected with the inlet of a gas-liquid separator of the absorption refrigeration unit, and the gas phase of the gas-liquid separator becomes low-pressure liquid through a condenser and an expansion valve, enters the inlet of the cold end of the evaporator, and enters the absorber after heat absorption and evaporation; the liquid phase of the gas-liquid separator is connected with the liquid phase inlet of the absorber through the stream heat exchanger, the concentration of the intermediate medium in the absorber becomes low after the intermediate medium is contacted and absorbed with steam, and the intermediate medium is connected with the cold end inlet of the generator through the stream heat exchanger to carry out process circulation.
According to the specific embodiment of the invention, the absorption refrigeration unit adopts a lithium bromide solution as an intermediate medium of the refrigeration cycle, the mass fraction of the lithium bromide concentrated solution is 60-65%, the lithium bromide concentrated solution becomes a dilute solution after absorbing water vapor, and the mass fraction of the lithium bromide dilute solution is 55-60%. The condenser and absorber of the absorption refrigeration unit use circulating cooling water as a cold utility, the generator absorbs heat above 90 ℃ from the compression condensation unit, and the evaporator generates low-temperature water at 7 ℃.
The waste heat refrigeration technology and the expansion cryogenic separation technology in the exhaust gas recovery system are coupled and embodied as follows: the export of a plurality of compressors of compression condensing unit is connected with absorption refrigeration unit generator hot junction entry, and the generator absorbs the heat of this unit, absorbs refrigeration unit, and the cold junction entry linkage of the 7 ℃ low temperature water that the evaporimeter produced and the multithread thigh heat exchanger of cryrogenic separation unit, after the cold volume of release, the multithread thigh heat exchanger of cryrogenic separation unit returns the rivers thigh of 12 ℃ to the evaporimeter of absorption refrigeration unit again, continues to produce 7 ℃ cold volume, carries out the flow circulation. By coupling the waste heat refrigeration technology and the expansion cryogenic separation technology, the heat waste of the compression condensation unit is reduced, the cold quantity requirement of the cryogenic separation unit is reduced, and the economic benefit is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following description of the invention is provided with accompanying drawings.
FIG. 1 shows a process flow diagram of a polyolefin plant vent gas recovery system coupling waste heat refrigeration technology and expansion cryogenic separation technology of the present invention.
Detailed Description
The technical solution in the embodiments of the present invention is clearly described below with reference to the accompanying drawings of the present invention. And the described embodiments are only some of the embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the system for recovering the exhaust gas of the polyolefin device coupled with the waste heat refrigeration technology and the expansion cryogenic separation technology provided by the invention comprises:
a compression condensing unit X for receiving an exhaust gas 1 from the polyolefin plant, recovering heavy hydrocarbon streams 2 and 3 in the exhaust gas, and outputting a remaining exhaust gas stream 7;
and the cryogenic separation unit Y receives the gas phase 7 of the compression and condensation unit, recovers a low-carbon hydrocarbon (ethylene is used as a main) stream 4, outputs a residual discharge gas stream (nitrogen is used as a main) 5 to participate in system nitrogen circulation, and transmits a part of residual discharge gas 6 to a plant torch in order to prevent the accumulation of low-carbon hydrocarbons in the discharge gas of the polyolefin plant.
And absorbing the refrigeration unit Z, recovering the compression heat of streams 8 and 9 of the compression condensation unit to prepare a low-temperature cold stream 12, and conveying the low-temperature cold stream to a multi-stream heat exchanger of the cryogenic separation unit to release cold.
In this embodiment, the compression condensing unit comprises two sets of compressor-condenser-gas-liquid separator mechanisms connected in series, the polyolefin plant discharge gas 1 is connected with the inlet of the compressor A1, the outlet of the compressor A1 is connected with the hot end inlet a1 of the generator D2 of the absorption refrigerating unit, the discharge gas is discharged from the hot end outlet a2 of the generator D2 after releasing heat higher than 90 ℃ through the generator D2 and is connected with the inlet of the condenser B1, the outlet of the condenser B1 is connected with the inlet of the gas-liquid separator C1, the gas-liquid separator C1 gas-phase outlet is connected in series with the next stage compressor A2-condenser B2-gas-liquid separator C2, similarly, the outlet of the compressor A2 is connected with the hot end inlet B1 of the generator D2 of the absorption refrigerating unit, after releasing heat, the discharge from the hot end outlet B2 of the generator D2 and returns to the condenser B2, the gas-liquid separator C2, the gas-liquid separators C1 and C2 were used for liquid phase recovery.
Specifically, the exhaust gas 1 is compressed to 0.45MPa by a compressor A1, the temperature is increased to 160 ℃, the temperature of the exhaust gas is reduced to 90 ℃ after heat exchange is carried out by a generator D2 of an absorption refrigeration unit, then the temperature is reduced by a condenser B1 and condensed to 40 ℃, the cooled exhaust gas is subjected to gas-liquid separation in a gas-liquid separator C1, and a stream 2 is liquid-phase high-carbon hydrocarbon and is recovered; and the residual exhaust gas enters a compressor A2, is compressed to 1.7MPa, is heated to 162 ℃, is subjected to heat exchange by a generator D2, is cooled to 90 ℃, is cooled to 40 ℃ by a condenser B2, is subjected to gas-liquid separation in a gas-liquid separator C2, is liquid-phase high-carbon hydrocarbons, and enters a gas-phase stream 7 of the gas-liquid separator C2 into a cryogenic separation unit.
In this embodiment, reciprocating compressors are used for the compressors a1 and a2, plate condensers are used for the condensers B1 and B2, and circulating cooling water is used for the cooling medium.
In this embodiment, the cryogenic separation unit comprises a multi-stream heat exchanger D1, a gas-liquid separator C3, an expander E1 and a throttle F1. The method comprises the steps that residual discharge gas 7 conveyed by a compression condensing unit is connected with a hot end inlet D1 of a multi-strand heat exchanger D1, a hot end outlet D2 of the multi-strand heat exchanger is connected with an inlet of a gas-liquid separator C3, a gas-liquid separator gas phase outlet is connected with a cold end inlet E1 of the multi-strand heat exchanger D1, a cold end outlet E2 is connected with an inlet of an expander E1, an outlet of the expander E1 is connected with a cold end inlet F1 of the multi-strand heat exchanger D1, after gas flow leaves from the cold end outlet F2, part of discharge gas stream 5 participates in system nitrogen circulation, residual discharge gas stream 6 goes to a torch to be subjected to tail gas treatment, a gas-liquid phase outlet of the gas-liquid separator C3 is connected with a multi-strand heat exchanger inlet g1 through a throttling valve.
Specifically, the residual exhaust gas 7 conveyed by a compression condensing unit exchanges heat with other 4 strands in a multi-strand heat exchanger D1, the temperature is reduced to-120 ℃, the residual exhaust gas enters a gas-liquid separator C3 for gas-liquid separation, a gas-phase stream (the main component is nitrogen) returns to the multi-strand heat exchanger D1 as a cold stream, the temperature is increased to-84 ℃, the gas-phase stream enters an expander E1, the pressure of the gas stream is reduced to 0.4MPa through the refrigeration action of the expander, the temperature is reduced to-130 ℃, the low-temperature gas stream is conveyed to a multi-strand heat exchanger D1 as a cold stream, the temperature is increased to 10 ℃ after cold energy is released, part of the gas stream 5 participates in system nitrogen circulation, the residual gas stream 6 is conveyed to a torch for tail gas treatment, the gas-liquid phase (the main component is low-carbon hydrocarbon) of the gas-liquid separator C3 is subjected to isenthalpic expansion to 0.4MPa through a throttle valve F7, the temperature is-123.3 ℃, the expansion ratio, heating to 20 ℃, and recovering a low-carbon hydrocarbon stream 4.
In this example, the multi-stream heat exchanger D1 was a shell and tube type multi-stream heat exchanger, and the expander was a turbo type expander. The temperature of the exhaust gas needs to be reduced to-120 ℃ to recover low-carbon hydrocarbons, and the cold energy is obtained from a-130 ℃ low-temperature stream obtained by gas phase expansion and temperature reduction and 7 ℃ low-temperature water output by a waste heat refrigerating unit.
According to a specific embodiment of the present invention, the absorption refrigeration unit comprises a generator D2, a gas-liquid separator C4, a condenser B3, a heat exchanger B4, two throttle valves F2 and F3, an evaporator H1, an absorber G1, and a centrifugal pump J1. A lithium bromide dilute solution stream 14 is connected with a cold end inlet C1 of a generator D2 to absorb heat from a compression condensation unit, a cold end outlet C2 of the generator D2 is connected with an inlet of a gas-liquid separator C4, a gas-liquid separator C4 gas-phase outlet is connected with an inlet of a condenser B3, an outlet of a condenser B3 is connected with an inlet of a throttle valve F2, an outlet of the throttle valve F2 is connected with a cold end inlet i1 of an evaporator H1, a cold end outlet i2 of the evaporator H1 is connected with a gas-phase inlet of an absorber G1, a hot end outlet j2 of the evaporator H1 is connected with a cold end inlet H1 of a multi-strand heat exchanger D1 of a cryogenic separation unit, and an outlet H2 of the multi-strand heat exchanger D1. The liquid phase outlet of the gas-liquid separator C4 is connected with a hot end inlet k1 of a heat exchanger B4, a hot end outlet k2 of the heat exchanger B4 is connected with an inlet of a throttle valve F3, an outlet of a throttle valve F3 is connected with a liquid phase inlet of an absorber G1, an outlet of the absorber G1 is connected with a cold end inlet m1 of a heat exchanger B4, and an outlet m2 of a cold end of the heat exchanger B4 is further connected with a cold end inlet C1 of a generator D2, so that the absorption.
Specifically, in this embodiment, a dilute lithium bromide solution stream 14 with a mass fraction of 57% enters a cold end of a generator D2 at a pressure of 0.00756MPa and a temperature of 74.6 ℃, absorbs heat of a compression condensation unit higher than 90 ℃, the temperature rises to 88.6 ℃, a part of solvent in the solution is vaporized to form water vapor, the molar fraction of the gas phase is 12%, the gas phase enters a gas-liquid separator C4 for gas-liquid separation, the gas phase stream (water vapor) enters a condenser B3 for cooling and condensation to 40.4 ℃, the gas phase stream enters a throttle valve F2, the pressure drop is 0.00087MPa, and the temperature drop is 4.8 ℃. After expansion of the throttle valve, the stream enters the cold end of an evaporator H1 for heat absorption evaporation, after leaving the evaporator H1, the stream is heated to 6.2 ℃, evaporated from liquid state to gaseous state, and then enters the water vapor inlet of an absorber G1, meanwhile, the hot end of the evaporator H1 is a 12 ℃ liquid water stream 13, after heat exchange of the evaporator, the liquid water stream 12 with the temperature of 7 ℃ is formed, the stream 12 enters the multi-stream heat exchanger D1 of the cryogenic separation unit again, after cold energy is released, the stream 13 is formed, and then the stream returns to the evaporator H1 for heat exchange, so that circulation is formed, and the cold energy with the temperature of 7 ℃ can be continuously generated and provided for the cryogenic separation unit. The liquid phase flow separated by the gas-liquid separator C4 is a lithium bromide concentrated solution with the mass fraction of 62%, the flow enters the hot end of a heat exchanger B4 for inter-flow heat exchange, the temperature is reduced to 45 ℃ from 88.6 ℃, the pressure is 0.00756MPa, the pressure is reduced to 0.00087MPa through a throttle valve F3, the flow enters an absorber G1 for reverse contact absorption with a water vapor flow, a lithium bromide dilute solution with the mass fraction of 57% is obtained after complete absorption, the temperature is 36.2 ℃, the lithium bromide dilute solution enters a centrifugal pump for pressurization, the pressure is increased to 0.00756MPa, the flow enters the cold end of a heat exchanger B4 for inter-flow heat exchange, the temperature is increased to 74.6 ℃, and the flow enters the cold end of a generator D2 to finish waste heat refrigeration cycle.
In this example, generator D2 used a shell and tube multiple-stream heat exchanger, condenser B3 used a plate condenser, and the cooling medium used circulated cooling water.
The embodiment realizes the same hydrocarbon recovery efficiency as the traditional process by the cooperative matching of the compression condensing unit, the cryogenic separation unit and the absorption refrigerating unit, and reduces the cost of cold quantity public engineering and the waste of waste heat. Wherein waste heat of the compression condensing unit is reduced by 60%, the efficiency of cold energy produced by the waste heat is 80%, and the cold utility of the embodiment completely uses the circulating cooling water with low price, thereby removing the use of the refrigerant.
The particular embodiments described above are illustrative of the present invention and are not to be construed as limiting, other modifications, specific methods, materials and embodiments of the invention which are within the scope of the appended claims are intended to be within the scope of the invention, which extends to all other methods and uses of the same functionality.

Claims (4)

1. A polyolefin device exhaust gas recovery system coupling a waste heat refrigeration technology and an expansion cryogenic separation technology is characterized by comprising:
a compression condensing unit for receiving the vent gas from the polyolefin plant, recovering heavy hydrocarbons in the vent gas, and outputting a residual vent gas stream;
the cryogenic separation unit receives the gas phase stream of the compression and condensation unit, recovers low-carbon hydrocarbons and outputs the residual discharge gas stream;
the absorption refrigeration unit is used for recovering the heat energy of the compression condensation unit, preparing low-temperature cold energy and conveying the low-temperature cold energy to the cryogenic separation unit;
the compression condensing unit comprises a two-stage or multi-stage compressor-condenser-gas-liquid separator process; in the process of the same stage of compressor-condenser-gas-liquid separator, the outlet of the compressor is connected with the inlet of the hot end of the generator of the absorption refrigeration unit, the heat released by the generator enters the condenser of the same stage, the outlet of the condenser is connected with the inlet of the gas-liquid separator, and the gas-liquid outlet of the gas-liquid separator is connected with the compressor of the next stage; the outlet of the polyolefin device is connected with the inlet of a compressor in the process of a first-stage compressor-condenser-gas-liquid separator; the gas-liquid separator in the last stage of compressor-condenser-gas-liquid separator process conveys the gas phase to the cryogenic separation unit;
the cryogenic separation unit comprises a multi-flow heat exchanger, a gas-liquid separator and an expander; the hot end inlet of the multi-strand heat exchanger is connected with the gas-phase outlet of the last stage of gas-liquid separator of the compression condensation unit, the hot end outlet of the multi-strand heat exchanger is connected with the gas-liquid separator inlet of the cryogenic separation unit, the gas-liquid separator gas-phase outlet of the cryogenic separation unit is connected with the expander inlet, the gas phase is expanded and cooled by the expander and then enters the cold end of the multi-strand heat exchanger, and after the cold energy is released, the gas phase is conveyed to a torch for tail gas treatment; the liquid phase outlet of the gas-liquid separator is connected with the other cold end inlet of the multi-flow heat exchanger through an expansion valve, and after the temperature is raised, the low-carbon hydrocarbons are collected;
the absorption refrigeration unit comprises a generator, a gas-liquid separator, a condenser, an evaporator, an absorber and a stream heat exchanger, wherein a middle medium in the absorption refrigeration unit is connected with a cold end inlet of the generator to absorb heat from the compression condensation unit; the outlet of the cold end of the generator is connected with the inlet of a gas-liquid separator of the absorption refrigeration unit, and the gas phase of the gas-liquid separator becomes low-pressure liquid through a condenser and an expansion valve, enters the inlet of the cold end of the evaporator, and enters the absorber after heat absorption and evaporation; the liquid phase of the gas-liquid separator is connected with the liquid phase inlet of the absorber through the stream heat exchanger, the concentration of the intermediate medium in the absorber becomes low after the intermediate medium is contacted and absorbed with steam, and the intermediate medium is connected with the cold end inlet of the generator through the stream heat exchanger to carry out process circulation.
2. The polyolefin plant vent gas recovery system of claim 1, wherein the generator of the absorption refrigeration unit is a multi-stream heat exchanger; and the low-temperature water at 7 ℃ generated by the evaporator of the absorption refrigeration unit is connected with the cold end inlet of the multi-strand heat exchanger of the cryogenic separation unit, after cold energy is released, the stream temperature is raised to 12 ℃, and then the stream returns to the evaporator of the absorption refrigeration unit to continuously generate the cold energy at 7 ℃, so that the process circulation is carried out.
3. The polyolefin plant vent gas recovery system of claim 1, wherein the vent gas in the cryogenic separation unit is expanded by an expander to a temperature between-125 ℃ and-130 ℃ and exchanges heat with the non-cryogenic vent gas to realize self cooling.
4. The polyolefin device vent gas recovery system of claim 1, wherein the absorption refrigeration unit uses a lithium bromide solution as an intermediate medium of the refrigeration cycle, the mass fraction of the lithium bromide concentrated solution before absorbing water vapor is 60% to 65%, and the mass fraction of the lithium bromide solution after absorbing water vapor is 55% to 60%.
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CN111059832B (en) * 2019-12-27 2024-09-13 青岛海尔智能技术研发有限公司 Refrigerating and freezing device
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